find all ocurrences for a command (in this case python) :

awk '{for(i = 11; i <= NF; i++) printf $i " "; printf "n"}' < <(ps aux | grep python)

kill all ocurrences for a command (python again) :

ps aux | grep python | awk {'print "kill " $2'} | bash

also can be added the -9 signal

ps aux | grep python | awk {'print "kill -9 " $2'} | bash

You can use awk to change the field separator in a data stream:

$ cat foo
a,b,c,d,e,f
a,b,c,d,e,f
$ awk 'BEGIN { FS = ","; OFS = ".."; } { $1 = $1; print }' foo
a..b..c..d..e..f
a..b..c..d..e..f

(You just have to touch one of the fields to get it to process the line.)

If you need to find the process hogging your CPU, try this:

$ ps aux | awk '!/root|nobody/ { if ($4>2) {print $2}}'

Given a log file with a date in the first column, chop up the file into separate file:

$ awk '/^[0-9]/ {print $0 > $1".log"}' logfile.txt

If you have a string that has characters that the shell won't like, you can do a substitution on them:

$ awk '{gsub("/","_",$1); print $1 > $1".log"}' logfile.txt

If you need to fetch a substring, but you have more than one delimiter, throw them all in there on the -F option to awk.

Given the text <VirtualHost 192.168.1.0:80>:

$ awk -F" |>" '/^<Virtual/ {print $2}'

Would return 192.168.1.0:80.

Adding line numbers to a file is easy if you use awk or grep. Adjust the padding in the printf (%2d) for the amount of padding:

awk '{no=no+1; printf "%2d : %s\n", no, $0}' filename > filename.out

Command line taken (and slightly modified) from the UGU mailing list; credit goes to pradeep@unixguru.zzn.com.

Use this command to purge old configs and files from your system that are in uninstalled packages:

$ dpkg --get-selections | awk '/deinstall/ {print $1}' | xargs dpkg --purge